Sending Unit has me stumped!

[Ryanz]

Originally Posted by pjmoreland

Could you upload a photo of the entire front of your multimeter getting the 125 reading?

Here you go - doing this from my phone so hoping it works. Tried changing resistor but didn’t change anything but I’m needing to see a pic of the back of someone else’s cluster to ensure I am installing it correctly.

[pjmoreland]

Your multimeter is reading 5V according to the 0-10 scale, which is what I'd expect to see if everything is working correctly.

The notches on the sides of the resistor can point either way. The C shaped contact patches need to face away from the gauge so that the nuts make contact with them. There are some photos in this thread.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

[Ryanz]

Originally Posted by pjmoreland

Your multimeter is reading 5V according to the 0-10 scale, which is what I'd expect to see if everything is working correctly.

The notches on the sides of the resistor can point either way. The C shaped contact patches need to face away from the gauge so that the nuts make contact with them. There are some photos in this thread.

https://67-72chevytrucks.com/vboard/...d.php?t=640615

Alright - well back to the drawing board. It still has to be a ground causing the issue somewhere doesn’t it? Dang this has been a source of frustration. I sure appreciate ALL of your help.

[pjmoreland]

A ground issue at the tank, a faulty connection between the sender and the gauge, or an excessively high resistance in your sender would explain it. I see no indication of any of those things.

[pjmoreland]

Could it be something as simple as you're not getting a good connection between the tan wire and your sender?

[Ryanz]

Originally Posted by pjmoreland

Could it be something as simple as you're not getting a good connection between the tan wire and your sender?

No that all seems to be okay. It connects strongly. And, as I said - it works outside the tank when I manually move the float and ground it to the cab. It’s like it won’t ground properly with the lock ring to tank. But then why wouldn’t a manual ground make it work when it’s in the tank. That’s the part that is baffling.

[pjmoreland]

I don't think the 5V voltage reading indicates a problem with your gauge. It sure seems like there is a lack of ground connection at your sender base.

Maybe try running a wire from the negative terminal of your battery to the sender base.

[Ryanz]

Originally Posted by pjmoreland

I don't think the 5V voltage reading indicates a problem with your gauge. It sure seems like there is a lack of ground connection at your sender base.

Maybe try running a wire from the negative terminal of your battery to the sender base.

Alright - update. I have figured out that I have it working inside, and outside the tank - but the reading on the gauge reads way over full (3 O'clock) with the float in full position. The ohms read 0-90 from empty to full, but the gauge goes from empty to way over full. Would that indicate I have a resistor issue on the back of gauge?

The reason I thought I was having a ground issue before is once I put it down deep in the tank it reads over full. But now I'm realizing as I'm lowering it in it moves from empty to full as it should (with ground wire attached to bolt on cab) but once I get it past a certain point my float goes high enough where the gauge reads well over full.

This is testing with new and old sending unit. Any thoughts before I put it all back together?

Thanks in advance - Ryan

[dmjlambert]

My thought is it wouldn't bother me. If it does the job of letting me know it has enough gas, or it's running out, that is all I would need to know. It may read better than a brand new Chinese gauge. I bought my latest instrument cluster from here in the parts section of the forum, and put together 1 better cluster from 2 that weren't so good. I'd rather get used parts than new when given a choice, but that's me.

[Ryanz]

Originally Posted by dmjlambert

My thought is it wouldn't bother me. If it does the job of letting me know it has enough gas, or it's running out, that is all I would need to know. It may read better than a brand new Chinese gauge. I bought my latest instrument cluster from here in the parts section of the forum, and put together 1 better cluster from 2 that weren't so good. I'd rather get used parts than new when given a choice, but that's me.

Ya, when I tested on my old cluster it only goes up to 1/4 - so I know that resistor isn’t any good. I was just curious if this resistor could be causing the opposite issue.

[pjmoreland]

The resistor on the back of the gauge should measure at around 90 Ohms. This measurement must be taken with the resistor removed from the gauge. If the resistor is significantly lower than 90 Ohms, then this will cause the gauge to read higher than usual.

If you have a reproduction gauge that has the resistor built into it and is intended to be used without an external resistor, then adding an external resistor will result in lower resistance and therefore higher gauge position (two resistors of the same value connected in parallel results in half the resistance).

[pjmoreland]

Take a look at the comment in this video at 2:36 about how the reproduction gauge doesn't use an external resistor.

https://youtu.be/Bq3YfCLq4So?t=156

[Ryanz]

Originally Posted by pjmoreland

Take a look at the comment in this video at 2:36 about how the reproduction gauge doesn't use an external resistor.

https://youtu.be/Bq3YfCLq4So?t=156

My new cluster worked for a year before the gauge acted up. So it shouldn’t be that it was because it came with a resistor.

[Ryanz]

Originally Posted by pjmoreland

The resistor on the back of the gauge should measure at around 90 Ohms. This measurement must be taken with the resistor removed from the gauge. If the resistor is significantly lower than 90 Ohms, then this will cause the gauge to read higher than usual.

If you have a reproduction gauge that has the resistor built into it and is intended to be used without an external resistor, then adding an external resistor will result in lower resistance and therefore higher gauge position (two resistors of the same value connected in parallel results in half the resistance).

No, it’s an all new cluster that worked fine for a year until the fuel gauge started acting up. But get this - I tested both resistors (the one in my new cluster and the one in my old cluster. Both measure 90 ohms. But when I put the old cluster in and hook it up the gauge won’t go past a 1/4, and when I put the new cluster in it goes way above full. The only think I’m realizing is I’m doing this without hooking the little ground clamp that comes off the cluster. Just plugging the cluster in and trying the key without installing them.

[pjmoreland]

If the ground clamp isn't grounded, then the winding in the gauge that pushes the gauge toward FULL will not work.

[Ryanz]

Originally Posted by pjmoreland

If the ground clamp isn't grounded, then the winding in the gauge that pushes the gauge toward FULL will not work.

Sorry, that was a stupid post. I was thinking that clamp was connected to each cluster but of course it’s not. Was having a Manitoba moment. It’s not been unhooked. So I’m still confused. Damn.